1. Field of the Invention
The present invention relates to a preparation of a cathode material for lithium ion cell and, more particularly, to a method of preparing a cathode material for lithium ion cell which is adequately used in miniaturized wireless devices such as camcorder, portable radiophone, notebook PC and the like with the cycle characteristic enhanced and a high initial discharge capacity.
2. Discussion of Related Art
With the rapid progress of electronic, communication and computer-related industries, miniaturized wireless devices, e.g., portable radiophones, notebook PCs, and so forth are recently in great demand and therefore more electrical cells are required to be used for these devices as a power source.
There are two types of cells in general; cells that have the durability only for a single use, and secondary cells reusable in succession by a charging and recently preferred in use.
Many studies and developments have been made on the secondary cells, especially, lithium ion cells which are reversible cells related to entrance and release of lithium ions and have a high voltage of 3-4 Volts with high energy density of 100 Wh/kg.
Lithium ion cells contain a separated plate which is disposed between the anode, cathode and cathode of carbon fiber to absorb and ionize the anode, current collector and Lithium ion and nonabsorbed electrolyte.
Lithium ion cells use an electrode material for cathode and cathode that provides reversible entrance/release of lithium ions during a charge/discharge. As for a cathode material, the oxides of transition metals of high cell potential, energy density and stability are very significant to use such as LiCoO.sub.2, LiNiO.sub.2 and LiMn.sub.2 O.sub.4. One of these oxides of transition metals, LiMn.sub.2 O.sub.4 has been considered to be the most useful material because of it is very inexpensive and causes no pollution to the environment relative to the other materials.
Particularly, lithium manganese oxide with a spinel structure which show a gentle discharge curve with high discharge potential and a slight self-discharge may be advantageous as a useful cathode active material in that they can be used in a wide range of operating temperature without causing pollution and produced from an abundant source.
Despite these advantages, there is a limit to spinel LiMn.sub.2 O.sub.4 in using as a cathode active material because spinel LiMn.sub.2 O.sub.4 has the discharge capacity decreased with the repeated charge/discharge cycles.
To overcome the problem, many studies have been made, for example, a method of repressing a rapid decrease in the discharge capacity according to the charge/discharge cycles by replacing Li or Mn in LiMn.sub.2 O.sub.4 with other ions, raising another problem in that the initial discharge capacity is reduced Reference: J. Electrochem. Soc., 138, 1991, 2859; J. Electrochem. Soc., 143, 1996, 3590; Solid State Ionics, 69, 1994, 59!.